RCC Column Interaction Diagrams

Input
Example

P-M interaction diagrams are generated for major and minor axes of rectangular columns subjected to bending moment and axial compression or tension for a range of reinforcement values.

The diagrams are constructed by locating the following points on the interaction diagram:

Pure axial compression
Decompression
Balanced point
Tension controlled limit (for ACI 318-02)
Pure bending
Pure axial tension

Linear interpolation is used up to decompression point. Points beyond this are calculated by increasing depth of neutral axis in small steps.

Configuration of longitudinal reinforcement is specified by the number of bars in each layer separated by a blank space.

For example, the layer-wise numbers of bars for the configuration shown here is 3 2 2 3 where the values refer to bars in the first (top-most), second, third and fourth layers.

Reinforcement may be input as

Area of all bars in sq. inches or sq. mm
Percentage of gross concrete area
Diameter of bars

For the 12"x24" (300x600 mm) column section shown above, reinforced with 1" (25mm) nominal dia bars, steel may be given as 7.854, 2.73% or #8 (4908, 2.73% or 25mm).

Multiple values, separated by a blank space may be entered for reinforcement.

Thus, for a preliminary assessment of column capacity, reinforcement may be entered as percentage of gross concrete area, 1% 2% 3% 4% whereas for selection of bars, reinforcement may be entered in terms of diameters, #6 #7 #8 16mm 20mm 25mm etc.

On output, P-M curves are displayed for each value of reinforcement.